Wireless antenna, lower dbi = better?

Kol · 23 Oct 2006 at 00:04

Hi guys,

I was thinking of buying some new antennae for my two wrt54gs so I can completely cover our house.

Am I better off going with a 5dBi or 7? There are ones even higher, but iirc the lower the value the better?

LewisStuart · 23 Oct 2006 at 00:20

Higher = better

Kol · 23 Oct 2006 at 10:35

Right ok, so I'd better off with something like an 18dBi ??

ganesh · 23 Oct 2006 at 17:59

Mikol said:
Right ok, so I'd better off with something like an 18dBi ??

18db is probably overkill by a huge margin. Unless you have a massive house. The majority of routers are supplied with 0-2db aerials so a 7db aerial should suffice, just remember for optimal coverage you should attach an aerial to your router and any pci wireless cards you have.

Pint · 23 Oct 2006 at 21:54

If you get them too high you'll actually make them too powerful for home use which is illegal.

Limit right now is 100mW and your router is supposed to autosense the signal strength but if the antennae are too strong then you'll go over the limit.

New limit of 10W is being proposed though.

Pulseammo · 23 Oct 2006 at 22:33

What firmware are you running? You can crank the power up a bit I do believe! I don't know if you need an new antenna to make use of it though.

bitslice · 23 Oct 2006 at 22:41

Pint said:
If you get them too high you'll actually make them too powerful for home use which is illegal.

I initially thought it was the transmit power of the device that was limited, not the ERP, but it seems you are right.

It seems there is a limit of about 12dB gain for an aerial to keep it within legal limits.
...not that it's hard to get a 24dB aerial if you really want one

yah learn something new every day
.

Kol · 23 Oct 2006 at 23:26

Cheers for the info guys, I'm using DD-WRT, which has an upper limit of 251mW (apparently - not sure whether this is true

) I could crank it up, but wasn't sure which was more reliable. Increasing the xmit power or just replacing both aerials on the router.

Our house has solid walls, and the signal can reach a fair way throughout, but the quality is pretty naff sometimes.

I'll have a look at some 7/12dBi, but consider the 18 ... thanks for everything lads.

ted34 · 23 Oct 2006 at 23:30

I got a 19dbi from sweden on a certain auction site. Its omni-directional and stick out window and network list goes crazy on a scan. Its combined with a netgear rangemax card. Think its a 2mile range in open area

bitslice · 23 Oct 2006 at 23:33

^^
likewise, I've tested a 10db panel aerial that's good for 500m.
I run it at 1/4 power for a 100m free space link.

.

Kol · 24 Oct 2006 at 14:27

Nice one. I'll invest in a couple of those. I can always turn the power right down.

norm · 24 Oct 2006 at 15:31

The higher the signal gain the tighter the signal beam.

So if you have a 19dBi omni-directional antenna like a poster above mentioned you will have to be on the exact same plane of height to get any reception from it. If you had this installed in your house for example and the antenna was on the first floor, you would get poor to nil reception downstairs.

Whereas a 0dBi omni-antenna will radiate in all directions equally, or at least in theory.

LewisStuart · 24 Oct 2006 at 17:08

Mikol said:
Cheers for the info guys, I'm using DD-WRT, which has an upper limit of 251mW

I wouldn't go more than 70mW, or you may damage your router.

Kol · 24 Oct 2006 at 19:11

LewisStuart said:
I wouldn't go more than 70mW, or you may damage your router.

Cheers for the info. Even increasing it to 56mW I was worried about and believed that should be my max. It's helped, but I do notice a fair few errors on the Tx side ??

bitslice · 25 Oct 2006 at 10:49

LewisStuart said:
I wouldn't go more than 70mW, or you may damage your router.

why?

if something is designed to pump out xxx mW, then setting it to that isn't going to damage anything....

although normally you would just increase power till you get a good signal
if the signal is still bad, just resite the aerial or get one with more gain.

maybe the OP could try a small panel high up in the loft, pointing down ?
That should cover all the floors.
(The loft is a good location as the signal is mostly travelling through plaster ceilings and not brick walls)

.